Cooler construction in a hot-gas engine



Oct. 2, 1956 DE LANGE r. 2,764,879

COOLER CONSTRUCTION IN A HOT-GAS ENGINE Filed Dec. 30, 1954 INVENTORLEENDERT D: LANGE AGENT United States Patent "ice 2,764,879 COOLERCONSTRUCTION IN A HOT-GAS ENGINE Leendert De Lange,

lands, assignor to Hartford.National Bank and Trust Company, Hartford,Conn., as trustee This invention relates to hot-gasreciprocatingapparatus comprising a space of low temperature anda spaceof high temperature, which spaces freely communicate with one another byway of a heater, a regenerator and a cooler, while their volumes may bevaried by means of one or more pistonlike bodies. A gas, the so calledworking medium, in the apparatus performs a closed thermodynamic cyclewhich gas always remains in the same state of aggregation.

The term hot-gas reciprocating apparatus is to be understood in thiscase to mean a hot-gas reciprocating motor, a refrigerator or a heatpump, the two last-mentioned operating on the reversed hot-gas motorprinciple. The refrigerator is frequently also termed cold-gasrefrigerator. Hot-gas reciprocating apparatus, as is wellknown, may beconstructed in different ways, for example as displacer apparatus, asdouble-operating apparatus, as apparatus having the cylinders at anangle to one another, or as apparatus in which the working space of acold-gas refrigerator is united with that of a hot-gas motor.

In such apparatus the heater constitutes the heat-exchanger in whichheat is supplied to the working medium of the apparatus, whereas heat isdissipated from the working medium in the cooler. It is also known thatdifferent media may be utilized in the apparatus. In the case of hot-gasmotors and heat pumps, use is commonly made of air as the workingmedium. In the case of coldgas refrigerators use may be made of air,nitrogen or oxygen, hydrogen or helium according to the purpose forwhich the apparatus is intended. Air may be used only if the temperatureat which the refrigerator must supply cold output is not unduly low and,for example, not lower than l40 C. If a cold-gas refrigerator mustsupply cold production at lower temperatures, hydrogen or helium must beutilized. In this case, the refrigerator may be of a construction suchthat a temperature of, for example 200 C. is reached.

According to the invention it has been found that in the cooler theratio between the length and the inner hydraulic diameter of the ductsmust be located within determined limits. It was found also that if theratio is smaller than the values specified below, the cooling action ofthe cooler becomes so small that the trans mission of heat from theworking medium in the apparatus to the walls of the ducts becomesinsuflicient. However, if the ratio is increased, the loss due to flowincreases to such an extent that although the transmission of heat isconsiderably improved, the specific capacity of the apparatus decreases.

Furthermore, it has been found that the limits are dependent upon thekind of the gas performing a thermodynamic cycle in the apparatus.

Further in accordance with the invention, the total length L of theducts in the cooler wherein L is at least 20 M- dh, and at the most 55M- dn, and wherein M=the molecular weight of the gas in the apparatusand dn=the inner hydraulic cross diameter of the ducts Emmasingel,Eindhoven, Netherfor the gas in the cooler.

2,764,879 Patented oer. 2 1956 2 The hydraulic diameter is four timesthe quotient of the surface and the periphery of the passage of a duct.If the cooler comprises two 'or more-portions located one after another,L represents the total distance between the inlet surface of one coolerand the outlet surface of the other cooler.

It will be evident that the molecular weight differs for the differentgases. Thus, the molecular weight is 2 forhydro'gen and 4 for" heliumwhile a molecular weight of 29 m'aybe assumed for air.

The above-mentioned limits apply to different types of coolers, forexample to pipe coolers and also to coolers with fins.

In order that the-invention may be readily carried into effect, it willnow be described with reference to the accompanyingdrawing, which" Fig.1 shows a cold-gas refrigerator of the displacer type and Fig. 2 showson an enlarged scale a horizontal section of part of a cooler.

The refrigerator comprises a cylinder 1, in which a displacer 2 and apiston 3 are adapted to move up and down with a substantially constantphase difference, the displacer acting upon the volume ,of a space 4which freely communicates with a space 8 through a freezer 5, aregenerator 6 and a cooler 7. The spaces 4 and 8 are frequently termedthe freezing space and the cooled space, respectively said space 8naturally being at a temperature higher than the temperature of space 4.

The displacer is coupled by means of a driving-rod system 9 to a crankof a crank-shaftll), whereas the piston is coupled by means of adriving-rod system 11 to cranks of the same crank-shaft 10.

The refrigerator is driven by an electric motor 12, so that the pistonand the displacer are moved up and down, substantially expansionoccurring in the space 4 and substantially compression occurring in thespace 8. A gas to be cooled, for example air, may be led along the fins17 provided on the outside of the freezer 5,While any condensateproduced may be discharged from the apparatus. The working medium usedin the apparatus itself may be, for example, hydrogen. The cooler 7 isof the type comprising fins 17. The cooling water is supplied to thecooler by way of a line 13 and discharged therefrom through a line 14.

In the refrigerator shown, the working medium used is hydrogen. If thehydraulic diameter of the duct 18 is 0.1 cm., L must be at least 20.2.0.1 cm.=2.3 cm. and at the most 55.2- .0.1=6.3 cm.

If, however, the refrigerator is operated with air, L must be locatedbetween different limits. In this case L is at least 20.29- .0.1 cm.=3.8cm. and at the most 55.29 .0.1 cm.=10.45 cm.

It is noted that the duct 18 having a hydraulic diameter of 0.1 cm. isobtained if the width 15:62.5 microns and the length l6=250 microns suchas with a duct 18 as given by way of example, in

shown in Fig. 2. In this embodiment, in which a large number of finsis'provided, the inner cross-section may without objections be regardedas a rectangle. However, if the number of fins or the radius ofcurvature of the wall of the cylinder should be small, it is preferableto calculate the surface and the periphery of the actual inner section.It will be evident that in the case of pipes having a circularcross-section, the hydraulic diameter is equal to the actual diameter ofthe pipe.

While I have shown and described the preferred embodiment of myinvention, it will be understood that the latter may be embodiedotherwise than as herein specifically illustrated or described and thatin the illustrated em- 3 parting from the underlying idea or principleof the invention within the scope of the appended claims.

What is claimed is:

1. A hot-gas reciprocating apparatus having a gas of invariable chemicalcomposition therein comprising a low temperature space, a space having atemperature higher than said low temperature space, a freezer, aregenerator and a cooler having ducts therein, cylinder means, twopistons reciprocating in said cylinder meansfsaid spaces communicatingwith each other through said cooler, freez er and regenerator while saidgas performs a closed thermodynamic cycle therein and the volume of saidgas being varied in said spaces by the said reciprocating pistons, thetotal length L of the ducts in the cooler being at least 20 M- d11,where M =the molecularweight of the gas in the apparatus and dh=thehydraulic diameter of said ducts for the gas in the cooler.

2. A hot-gas apparatus as setfo'rth in claim 1 wherein L is between 20M- dh and 55 M -db.

3. A hot-gas reciprocating apparatus having a gas of invariable chemicalcomposition which is subjectto* a closed thermodynamic cyclic process inwhichthe gas is invariably the same physical state comprising; at leastone cylinder; a crankshaft; at least one piston in said cylinderconnected to said crankshaft; said cylinder having a chamber on one sideof said piston with a relatively low temperature, and a chamber onanother side of said piston having a temperature higher than said firstchamber; said chambers varying continuously in volume; and meansconnecting said chamber of relatively low temperature with said chamberof relatively high temperature; said means comprising a' freezer, aregenerator, and a cooler provided with ducts and connected in series;the total-length L of the ducts in the cooler being at least 20 M dh,where M =the molecular weight of the gas in the apparatus and dh=thehydraulic diameter of said cooler ducts.

References Cited in the file of this patent UNITED STATES PATENTS2,011,964 Aug. 20, 1935

